1. Field of the Invention
The present invention relates generally to an internal combustion engine and more specifically to an improved cylinder block construction which both improves the structural rigidity and cooling efficiency thereof.
2. Description of the Prior Art
In a conventional liquid cooled multi cylinder internal combustion engine cylinder block such as shown in FIG. 1 of the drawings, a suitable coolant such as water is forcefully circulated through the cylinder block 1, cooled in an air cooled heat exchanger or radiator (not shown) and recirculated back into the cylinder block 1. However, in such arrangements it is necessary, in order to achieve uniform cooling of the cylinders 2, to provide free fluid flow within the coolant jacket both between and around same. This introduces a problem in that the reinforcing interconnections between the cylinders 2 (which are cylindrical and structurally rigid) and the outer wall 3 of the cylinder block (which is flat and relatively flexible) are limited whereby the structural rigidity of the outer wall of the cylinder block tends to be inadequate. Accordingly, the wall tends to vibrate, especially under given modes of engine operation, and thus defines a source of noise.
In order to overcome this problem it has been proposed to use ribs and/or bolts to provide a partial connection between the cylinders and the outer wall. However, excessive use of same obstructs coolant flow undesirably. Further, the shape and location of the ribs is severely limited due to the internal flow requirement mentioned above. Accordingly, an engine block having a coolant jacket wall featuring a suitable level of rigidity has been difficult to obtain especially while maintaining the weight of same at a suitably low level.
More recently, a radically different type of engine cooling system such as shown in FIG. 2 of the drawings has been proposed. This system is disclosed in European Patent Application No. 0 059 423, published on Sept. 8, 1982. This system basically features an arrangement wherein the coolant in the coolant jacket 4 defined in the cylinder block 5, is permitted to boil and the gaseous and/or boiling coolant passed out through the cylinder head 6 to a compressor 7. The compressor 7 compresses the gaseous coolant raising the temperature and pressure thereof and pumps same into an air cooled heat exchanger (radiator) 8. Due to the high temperature differential between the atmosphere and the high temperature-pressure vapour, the cooling efficiency of this arrangement is remarkably high. Subsequent to condensation the coolant is recirculated back into the cylinder block by way of a reservoir 9 (including a liquid level sensor 10) and an expansion valve 11.